Thermosetting coating compositions

ABSTRACT

Provided are polyester resins containing hydroxy functionalized isophthalate ester moieties useful in coating compositions. The invention provides both solvent-borne as well as water-borne coating compositions comprised of the resins and a crosslinker such as a melamine-type crosslinker. Polyester resins of the present invention having a T 8  of greater than about 50° C. are useful in thermosetting powder coating compositions. The coatings thus provided possess excellent acid resistance, hardness, impact resistance, and stain resistance.

This is a divisional application of copending application Ser. No.07/982 545 filed on Nov. 27, 1992 pending.

FIELD OF THE INVENTION

This invention belongs to the field of polyester chemistry. Inparticular, this invention relates to polyester resins having hydroxyfunctional isophthalate ester moieties and to thermosetting coatingcompositions comprised of such resins.

BACKGROUND OF THE INVENTION

U.S Pat. No. 3,381,058 discloses the use of hydroxyaromatic dicarboxylicacids (e.g. 5 hydroxyiso-phthalic acid) in preparing polyesters whichhave improved dyeability with basic and direct dyes. The polyestercompositions disclosed in this patent are useful as fibers, but not asresins for producing coatings when crosslinked.

It is known (EP 0,419,088) that polyester resins containing terminalhydroxy groups may be capped by reacting with carboxyphenols (e.g.p-hydroxy benzoic acid) to give terminal groups such as I ##STR1##wherein R₁ is a direct bond, C₁ -C₂₀ hydrocarbylene or C₁ -C₂₀oxyhydrocarbylene and R₂ is hydrogen, hydroxy, halo, C₁ -C₄ alkyl, C₁-C₄ alkoxy or C₁ -C₄ aIkoxycarbonyl and that said resins may becrosslinked to produce coatings having enhanced properties. It is notedthat the hydroxy functionalized benzoate moieties in these knowncompositions are monovalent--the hydroxy group is not reactive under theconditions employed for resin synthesis--and always in terminalpositions on the polymer chain, in contrast to the hydroxyfunctionalized aromatic diester moieties of this invention which aredivalent which are located randomly along the polymer chain as inherentstructural units.

Lastly, it is known (Eastman Kodak Publication No. N 278, "ResinFormulations from Eastman Industrial Chemicals", May 1981) that valuablecoatings can be prepared from polyester resins similar to those of thisinvention but without containing the hydroxy functionalized isophthalateester moieties, the structural unit which characterizes the valuableresins/coatings of this invention. The previously known coatings haveshown deficiencies in the properties of hardness, acid resistance andstain resistance, etc.

There is a need in the coatings industry for high strength, highmodulus, chemically resistant coatings. This invention is directedtoward meeting the above needs and the coatings described haveimprovements in one or more specific properties of acid resistance,pencil hardness, impact resistance, solvent resistance, gloss, etc.

The present invention provides polyester resin compositions containinghydroxy functionalized isophthalate moieties, said resins being preparedby a direct polycondensation process which is suitable for economical,large scale production. These new resins are useful as coatings bindersand may be dissolved in conventional solvents and formulated intothermosetting coating compositions which exhibit a good combination ofthe desirable properties mentioned above.

SUMMARY OF THE INVENTION

The present invention provides polyester resins containing hydroxyfunctionalized diester aromatic moieties. In a preferred embodiment ofthe present invention, 5 -hydroxyisophthalic acid residues areincorporated into such curable polyesters. The curable polyesters of thepresent invention are useful in thermosetting coating compositions. Theinvention provides both solvent borne as well as water-borne coatingcompositions comprised of the curable polyesters and a crosslinker suchas an amino or melamine-type crosslinker. The coatings thus providedpossess excellent acid resistance, hardness, impact resistance, andstain resistance.

The curable polyesters of the present invention are also useful inthermosetting powder coating compositions.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a curable polyester comprised of fromabout 10 mol % to about 20 mol % of a hydroxy functionalized diacidcomponent corresponding to Formula (II) ##STR2## wherein X is selectedfrom --O--, --S--, --SO₂ -- or --O(CH₂)--_(n) ; wherein n is an integerfrom about 1 to about 6; R is a phenyl radical containing from 1 to 3hydroxy groups, with the proviso that when X is --O-- that R may behydrogen. The phenyl radical may be further substituted with one or moregroups selected from C₁ -C₄ alkyl, C₁ -C₄ alkoxy or halogen. As apreferred embodiment of the present invention, X is --O-- and R ishydrogen. In a more preferred embodiment, the --X--R group is in the5-position.

We have discovered that when a curable polyester contains structuralunits derived from (II) that said polyester can be used to preparecoatings having improved properties when crosslinked with conventionalcrosslinking agents such as a melamine formaldehyde type crosslinker.

The curable polyester resins of this invention may have terminal endgroup compositions which are hydroxyl enriched or carboxyl enriched byvarying the ratio of polyester reactants. The enamel compositionsprovided may be either solvent borne or water borne. Water-bornecompositions are provided by incorporating a polybasic acid such astrimellitic acid in the preparation of the curable polyester resin toproduce a carboxyl enriched composition which is then neutralized withan amine and dispersed with water. Alternatively, a hydroxyl enrichedpolyester composition may be reacted with polybasic acids/anhydridessuch as trimellitic acid, trimellitic anhydride or phthalic anhydride toproduce a carboxy enriched curable polyester which can be furtherneutralized with an amine, e.g. N,N-dimethylamino -ethanol, triethylamine or ammonia. For the preparation of water-borne enamel compositionsit is desirable that the curable polyester resin have an acid number offrom about 40 to about 80 as determined by ASTM method D1639.

In one embodiment of this invention there is provided a curablepolyester having a number average molecular weight of about 800 to about6,000 and a weight average molecular weight of about 3,000 to about40,000, comprising

(a) about 20 to about 60 mol % of diol residues, based on the totalmoles of components (a), (b), (c), (d), (e) and (f);

(b) 0 to about 20 mol % of polyol residues, based on the total moles ofcomponents (a), (b), (c), (d), (e) and (f);

(c) about 5 to about 40 mol % of hydroxy functionalized isophthalic acidresidues, based on the total moles of (a), (b), (c), (d), (e) and (f);said hydroxy functionalized residues having the formula ##STR3## whereinX is selected from --O--, --S--, --SO₂ -- or --O--(CH₂ --)_(a) (n is 1to about 6); R is a phenyl radical containing 1--3 hydroxy groups withthe proviso that when X is --O-- or --S--, that R may also be hydrogen;

(d) about 10 to about 40 mol % of diacid residues, derived from anaromatic diacid or a cycloaliphatic diacid or a mixture thereof, basedon the total moles of (a), (b), (c), (d), (e) and (f);

(e) about 0 to about 40 mol % of diacid residues derived from analiphatic diacid, based on the total moles of components (a), (b), (c),(d), (e) and (f);

(f) 0 to about 10 mol % of residues derived from trimellitic acid ortrimellitic anhydride, based on the total moles of components (a), (b),(c), (d), (e) and (f).

In a preferred aspect of this embodiment of the present invention, it ispreferred that component (d) residues be comprised of at least 50 mole %of residues of isophthalic acid.

In another embodiment of the invention there is provided an enamelcomposition comprising

(I) about 25 to about 65 weight % of the curable polyester describedimmediately above; based on the total weight of components I, II, andIII;

(II) about 5 to about 20 weight % of an amino crosslinking agent, basedon the total weight of (I), (II) and (III);

(III) about 20 to about 70 weight % of an organic solvent, based on thetotal weight of (I), II and III, the total being 100%.

In another embodiment of the invention there is provided a water-borneenamel composition comprising

(I) about 25 to about 65 weight % of the curable polyester describedabove, based on the total weight of components (I), (II), (III) and(IV); wherein said polyester, if having an acid number of 40 or less, ismodified by treatment with a polybasic acid to yield a modifiedpolyester having an acid number of about 40 to 80, followed by treatmentof the polyester or modified polyester with about 1 to about 4 weightpercent of an amine;

(II) about 0 to about 10 weight % of a water-miscible organic solvent,based on the total weight of (I), (II), (III), and (IV);

(III) about 30 to about 70 weight %, based on the total weight of (I),(II), (III), and (IV);

(IV) about 0 to about 20 weight % of a cross-linking agent, based on thetotal weight of (I), (II), (III), and (IV).

The curable polyesters of the present invention having a glosstransition temperature (T₈) of greater than about 50° C. may beformulated into thermosetting powder coating compositions. Thus, thepresent invention also provides a thermosetting powder coatingcomposition comprising

(I) about 70 to 95 weight percent of the curable polyester of thepresent invention, having a T₈ greater than about 50° C., based on thetotal weight of (I) and (II); and

(II) about 5 to about 30 weight percent of a cross-linking agent, basedon the total weight of (I) and (II).

Diol components useful in the practice of the invention include ethyleneglycol; propylene glycol; 1,3-propanediol; 2,4-dimethyl 2-ethyl hexane1,3-diol; 2,2-dimethyl 1,3-propanediol; 2-ethyl 2-butyl 1,3-propanediol;2-ethyl 2-isobutyl 1,3-propanediol; 1,3-butanediol; 1,4 butanediol;1,5-pentanediol, 1,6-hexanediol; 2,2,4 -trimethyl 1,3-pentanediol;thiodiethanol; 1,2 cyclohexanedimethanol; 1,3-cyclo -hexanedimethanol;1,4 cyclohexanedimethanol; 2,2,4,4-tetramethyl-1,3-cyclobutanediol;p-xylylenediol; diethylene glycol, triethylene glycol; tetraethyleneglycol; and pentaethylene, hexaethylene, heptaethylene, octaethylene,nonaethylene, and decaethylene glycols. The most highly preferred diolis 2,2 dimethyl 1,3-propanediol.

Preferred polyols include trimethylolpropane, trimethylolethane,glycerol, 2,2 bis(hydorxymethyl) 1,3-propanediol, 1,2,3,4,5,6hexahydroxy hexane, bis(2,2-bis(hydroxymethyl) 3 propanol ether, and thelike. Trimethylolpropane is the most highly preferred polyol.

Preferred hydroxy functionalized isophthalic acids include the followingcompounds which correspond to Formula II) above: ##STR4##

It is preferred that the isophthalic acid compounds above be hydroxyfunctionalized in the 5-position and 5-hydroxyisophthalic acid isfurther preferred.

Examples of aromatic diacid components include isophthalic, phthalic,terephthalic, diphenic, 4,4'-oxydibenzoic, 4,4' sulfonyldibenzoic,4,4'-biphenyldicarboxylic and naphthalenedicarboxylic acids, withisophthalic acid being particularly preferred.

Examples of aliphatic diacid components include linear straight orbranched chain saturated aliphatic diacids including oxalic, malonic,dimethylmalonic, succinic, glutaric, adipic, trimethyladipic, pimelic,2,2-dimethylglutaric, azelaic and sebacic acids and unsaturatedaliphatic diacids including fumaric, maleic and itaconic acids. Adipicacid is highly preferred.

Examples of cycloaliphatic diacid components include1,2-cyclohexanedicarboxylic acid, or anhydride,1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexane -dicarboxylic acid,and 1,3-cyclopentanedicarboxylic acid, with ,1,4-cyclohexanedicarboxylicacid being highly preferred.

It should be appreciated that the lower alkyl, i.e., C₁ -C₆ alkyl, esterderivatives of the above mentioned acids may be utilized in thepolyester producing condensation.

In the preparation of the water-borne enamel compositions above, thecurable polyester is further reacted with a polybasic acid (oranhydride) to give a carboxy enriched composition having an acid numberof at least 40, followed by neutralization of the carboxy groups byreacting with amines and dispersing in water. Useful polybasic acidsand/or anhydrides include trimellitic anhydride, trimellitic acid,phthalic acid, phthalic anhydride, citric acid, succinic anhydride,succinic acid and the like. Typical amines include ammonia,trimethylamine, diethylamine, monoethanolamine, monoisopropanolamine,morpholine, ethanolamine, diethanolamine, triethanolamine, N,N-dimethyl-ethanolamine, N, N-diethylethanolamine, N-methyl -diethanolamine andthe like. Curable polyesters having an acid number higher than 40 can beneutralized directly without the subsequent reaction of the polyesterresin with the polybasic acid or anhydride followed by neutralization.The resulting polymer with hydrophilic ammonium-salt end groups can thenbe dispersed in water to produce water borne enamel composition. Thisconventional amine-neutralization method has already been described byothers in considerable detail (see, for example, Olding and Hayward,Ed., "Resins for Surface Coatings", Volume III, SITA Technology, London,1987, p 182).

It will be appreciated, of course, that in the above description and asdescribed below, the various mole and weight percentages in the enamelcompositions and curable polyesters will always total 100 percent.

Suitable solvents for the curable enamel composition include xylenes,cyclohexanone, ketones, (for example, methyl amyl ketone),2-butoxyethanol, ethyl 3-ethoxypropionate, toluene, n-butanol, and othervolatile inert solvents typically used in industrial baking (i.e.,thermosetting) enamels.

Suitable co-solvents for the water-borne compositions of the presentinvention include ethanol, n-propanol, isopropanol, n butanol,sec-butanol, isobutanol, ethylene glycol monobutyl ether, propyleneglycol n-butyl ether, propylene glycol methyl ether, propylene glycolmonopropyl ether, dipropylene glycol methyl ether, diacetone alcohol,and other water-miscible solvents.

The "amino cross linking agent" is preferably a melamine-formaldehydetype cross linking agent, i.e., a cross-linking agent having a pluralityof --N(CH₂ OR³)₂ functional groups, wherein R³ is C₁ -C₄ alkyl,preferably methyl.

The cross-linking agent may also be a modified melamine-formaldehydetype resin such as toluene sulfonamide modified melamine-formaldehyderesins, and the like.

In general, the cross linking agent may be selected from compounds ofthe following formulae, wherein R³ is independently C₁ -C₄ alkyl:##STR5## In this regard, preferred cross-linking agents includehexamethoxymethylmelamine, tetramethoxymethylbenzoguanamine,tetramethoxymethylurea, mixed butoxy/methoxy substituted melamines, andthe like. The most preferred cross-linking agent ishexamethoxymethylmelamine. Alternatively, a toluene sulfonamidemethylated melaminformaldehyde resin powder may be utilized as across-linking agent.

In the case of thermosetting powder coating compositions, preferredcross-linking agents include cross-linking compounds with epoxy groups.Further, the carboxy functional curable polyesters of the presentinvention may be blended with an epoxy resin and, optionally, in thepresence of another epoxy functional compound such as triglycidylisocyanurate, and cured. Preferred epoxy functional compounds generallyhave a molecular weight of about 300 to about 4000, and haveapproximately 0.05 to about 0.99, epoxy groups per 100g of resin(i.e.,100-2000 weight per epoxy (WPE)). Such resins are widely known and arecommercially-available under the EPON® tradename of the Shell ChemicalCompany, the ARALDITE® tradename of CIBA-Geigy, and D. E. R. resins ofthe Dow Chemical Company.

Alternatively, the crosslinking agent may be a glycouril type. Ingeneral, such crosslinking agents possess a plurality of -N-CH₂ ORgroups with R═C₁ -C₈ alkyl, such as one sold by American Cyanamid asPOWDERLINK™ 1174 having the formula ##STR6##

As a further aspect of the present invention, there is provided acurable enamel composition further comprising one or more cross-linkingcatalysts. Examples of such catalysts include p-toluenesulfonic acid,the NACURE™ 155, 5076, and 1051catalysts sold by King Industries, BYK®Catalyst 450, 470, available from BYK-Chemie U. S. A., methyl tolylsulfonimide, and the like.

As a further aspect of the present invention there is provided across-linkable enamel composition as described above, further comprisingone or more leveling, rheology, and flow control agents such assilicones, fluorocarbons or cellulosics; flatting agents; pigmentwetting and dispersing agents; surfactants; ultraviolet (UV) absorbers;UV light stabilizers; tinting pigments; defoaming and antifoamingagents; anti-settling, anti-sag and bodying agents; anti-skinningagents; anti-flooding and anti-floating agents; fungicides andmildewicides; corrosion inhibitors; thickening agents; or coalescingagents.

Specific examples of such additives can be found in Raw Materials Index,published by the National Paint & Coatings Association, 1500 RhodeIsland Avenue, N. W., Washington, D. C. 20005.

Examples of flatting agents include synthetic silica, available from theDavison Chemical Division of W. R. Grace & Company under the trademarkSYLOID®; polypropylene, available from Hercules Inc., under thetrademark HERCOFLAT®; synthetic silicate, available from J. M. HuberCorporation under the trademark ZEOLEX®.

Examples of dispersing agents and surfactants include sodiumbis(tridecyl) sulfosuccinnate, di(2-ethyl hexyl) sodium sulfosuccinnate,sodium dihexylsulfo -succinnate, sodium dicyclohexyl sulfosuccinnate,diamyl sodium sulfosuccinnate, sodium diisobutyl sulfo-succinnate,disodium iso-decyl sulfosuccinnate, disodium ethoxylated alcohol halfester of sulfosuccinnic acid, disodium alkyl amido polyethoxysulfosuccinnate, tetra-sodium N-(,1,2-dicarboxy-ethyl) N-octadecylsulfo-succinnamate, disodium N-octasulfosuccinnamate, sulfatedethoxylated nonylphenol, 2-amino-2-ethyl-1-propanol, and the like.

Examples of viscosity, suspension, and flow control agents includepolyaminoamide phosphate, high molecular weight carboxylic acid salts ofpolyamine amides, and alkyl amine salt of an unsaturated fatty acid, allavailable from BYK Chemie U. S. A. under the trademark ANTI TERRA®.Further examples include polysiloxane copolymers, polyacrylate solution,cellulose esters, hydroxyethyl cellulose, hydro -phobically-modifiedhydroxyethyl cellulose, hydroxy -propyl cellulose, polyamide wax,polyolefin wax, carboxymethyl cellulose, ammonium polyacrylate, sodiumpolyacrylate, and polyethylene oxide.

Several proprietary antifoaming agents are commercially available, forexample, under the trademark BRUBREAK of Buckman Laboratories Inc.,under the BYK® trademark of BYK Chemie, U. S. A., under the FOAMASTER®and NOPCO® trademarks of Henkel Corp./Coating Chemicals, under theDREWPLUS® trademark of the Drew Industrial Division of Ashland ChemicalCompany, under the TROYSOL® and TROYKYD® trademarks of Troy ChemicalCorporation, and under the SAG® trademark of Union Carbide Corporation.

Examples of fungicides, mildewicides, and biocides include4,4-dimethyloxazolidine, 3,4,4-trimethyl -oxazolidine, modified bariummetaborate, potassium N -hydroxy-methyl-N-methyldithiocarbamate,2-thiocyano -methylthio) benzothiazole, potassium dimethyl dithio-carbamate, adamantane, N-(trichloromethylthio) phthalimide,2,4,5,6-tetrachloroisophthalonitrile, orthophenyl phenol,2,4,5-trichlorophenol, dehydroacetic acid, copper naphthenate, copperoctoate, organic arsenic, tributyl tin oxide, zinc naphthenate, andcopper 8-quinolinate.

Examples of U. V. absorbers and U. V. light stabilizers includesubstituted benzophenones, substituted benzotriazoles, hindered amines,and hindered benzoates, available from American Cyanamide Company underthe tradename Cyasorb UV, and available from Ciba Geigy under thetradename Tinuvin, and diethyl-3-cetyl- 4-hydroxy-benzyl-phosphonate,4-dodecyloxy-2-hydroxy benzophenone, and resorcinol monobenzoate.

Such paint or coating additives as described above form a relativelyminor proportion of the enamel composition, preferably about 0.05 weight% to about 5.00 weight %.

As a further aspect of the present invention, there is provided acurable enamel composition optionally containing one or more of theabove-described additives, further comprising one or more pigments.

Pigments suitable for use in the enamel compositions envisioned by thepresent invention are the typical organic and inorganic pigments,well-known to one of ordinary skill in the art of surface coatings,especially those set forth by the Colour Index, 3d Ed., 2d Rev., 1982,published by the Society of Dyers and Colourists in association with theAmerican Association of Textile Chemists and Colorists. Examples includebut are not limited to the following: CI Pigment White 6 (titaniumdioxide); CI Pigment Red 101 (red iron oxide); CI Pigment Yellow 42, CIPigment Blue 15, 15:1, 15:2, 5:3, 15:4 (copper phthalocyanines); CIPigment Red 49:1, and CI Pigment Red 57:1.

Upon formulation as described above, the curable enamel composition isthen applied to the desired substrate or article, e.g., steel, aluminum,or galvanized sheeting (either primed or unprimed), heated (i.e., cured)to a temperature of about 130° C. to about 175° C., for a time period of5-60 minutes and subsequently allowed to cool. Thus, as a further aspectof the present invention, there is provided a shaped or formed articlewhich has been coated with the thermosetting coating compositions of thepresent invention and cured.

Further examples of typical application and curing methods can be foundin U.S. Pat. Nos. 4,737,551 and 4,698,391, incorporated herein byreference.

As a further aspect of the present invention, there is provided acoating which results from the application and curing of the curableenamel composition as set forth above.

The powder coating compositions of this invention are preferablyprepared from the compositions described herein by dry mixing and thenmelt blending component (I) and the cross linking compound (II), and across-linking catalyst, along with other additives commonly used inpowder coatings, and then grinding the solidified blend to a particlesize, e.g., an average particle size in the range of about 10 to 300microns, suitable for producing powder coatings. For example, theingredients of the powder coating composition may be dry blended andthen melt blended in a Brabender extruder at 90° to 130° C., granulatedand finally ground. The melt blending should be carried out at atemperature sufficiently low to avoid premature cross-linking of thecomposition.

Typical of the additives which may be present in the powder coatingcompositions include benzoin, flow aids or flow control agents which aidthe formation of a smooth, glossy surface, stabilizers, pigments anddyes.

The powder coating compositions preferably contain a flow aid, alsoreferred to as flow control or leveling agents, to enhance the surfaceappearance of cured coatings of the powder coating compositions. Suchflow aids typically comprise acrylic polymers and are available fromseveral suppliers, e.g., Modaflow from Monsanto Company and Acronal fromBASF. Other flow control agents which may be used include Modarez MFPavailable from Synthron, EX 486 available from Troy Chemical, BYK 360Pavailable from BYK Mallinkrodt and Perenol F-30-P available from Henkel.An example of one specific flow aid is an acrylic polymer having amolecular weight of about 17,000 and containing 60 mole percent2-ethylhexyl methacrylate residues and about 40 mole percent ethylacrylate residues. The amount of flow aid present may preferably be inthe range of about 0.5 to 4.0 weight percent, based on the total weightof the resin component, and the cross-linking agent.

The powder coating compositions may be deposited on various metallic andnon-metallic (e.g., thermo-plastic or thermoset composite) substrates byknown techniques for powder deposition such as by means of a powder gun,by electrostatic deposition or by deposition from a fluidized bed. Influidized bed sintering, a preheated article is immersed into asuspension of the powder coating in air. The particle size of the powdercoating composition normally is in the range of 60 to 300 microns. Thepowder is maintained in suspension by passing air through a porousbottom of the fluidized bed chamber. The articles to be coated arepreheated to about 250° to 400° F. (about 121° to 205° C.) and thenbrought into contact with the fluidized bed of the powder coatingcomposition. The contact time depends on the thickness of the coatingthat is to be produced and typically is from 1 to 12 seconds. Thetemperature of the substrate being coated causes the powder to flow andthus fuse together to form a smooth, uniform, continuous, uncrateredcoating. The temperature of the preheated article also effectscross-linking of the coating composition and results in the formation ofa tough coating having a good combination of properties. Coatings havinga thickness between 200 and 500 microns may be produced by this method.

The compositions also may be applied using an electrostatic processwherein a powder coating composition having a particle size of less than100 microns, preferably about 15 to 50 microns, is blown by means ofcompressed air into an applicator in which it is charged with a voltageof 30 to 100 kV by high-voltage direct current. The charged particlesthen are sprayed onto the grounded article to be coated to which theparticles adhere due to the electrical charge thereof. The coatedarticle is heated to melt and cure the powder particles. Coatings of 40to 120 microns thickness may be obtained.

Another method of applying the powder coating compositions is theelectrostatic fluidized bed process which is a combination of the twomethods described above. For example, annular or partially annularelectrodes are mounted in the air feed to a fluidized bed so as toproduce an electrostatic charge such as 50 to 100 kV. The article to becoated, either heated, e.g., 250° to 400° F., or cold, is exposedbriefly to the fluidized powder. The coated article then can be heatedto effect cross-linking if the article was not preheated to atemperature sufficiently high to cure the coating upon contact of thecoating particles with the article.

The powder coating compositions of this invention may be used to coatarticles of various shapes and sizes constructed of heat-resistantmaterials such as glass, ceramic and various metal materials. Thecompositions are especially useful for producing coatings on articlesconstructed of metals and metal alloys, particularly steel articles. Asnoted above, since the compositions provided by the present inventioncure at a temperatures of as low as 115° C., it is also possible to coatmany thermoplastic and thermosetting resin compositions with thecompositions of the present invention.

Further examples of formulation methods, additives, and methods ofpowder coating application may be found in User's Guide to PowderCoating. 2nd Ed., Emery Miller, editor, Society of ManufacturingEngineers, Dearborn, (1987).

Experimental Section Example 1 -Preparation of Hydroxy Terminated Resin

To a three necked round bottom flask equipped with a mechanical stirrer,a steam partial condenser, a Dean-Stark trap, and a water condenser werecharged the following materials: neopentyl glycol (NPG) (86.82 g, 0.83mole), trimethylolpropane (TMP) (7.98 g, 0.06 mole), isophthalic acid(IPA) (64.02 g, 0.39 mole), 5-hydroxyisophthalic acid (HIPA) (46.22 g,0.25 mole), adipic acid (AD) (29.20 g, 0.20 mole) and 0.20 g of FASCAT4100 catalyst (Atochem North America, Inc). The mixture was heated to150° C. and stirred under a nitrogen atmosphere. The temperature wasthen gradually increased to 200° C. and held for about 4.5 hours anddistillate collected in the Dean-Stark trap. The resulting viscous resinwas collected in a metal container and cooled to room temperature. Theresin has the following composition based on the mol % of the componentspresent: NPG (48.0%), TMP (3.5%), IPA (22.5%), HIPA (14.4%) and AD(11.6%).

Example 2-Preparation of Enamel 1

The hydroxy enriched resin from Example 1 (20.0 g) was dissolved in 40mL of a solvent mixture [55% xylene, 32% methyl n-amyl ketone (MAK),6.5% ethyl 3-ethoxy -propionate (EEP) and 6.5% butyl alcohol by weight].To this solution were added 5 g of a crosslinking agent,hexamethoxymethyl melamine, CYMEL 303 (American Cyanamid), an acidcatalyst (0.38 g of a 40% p-oluene -sulfonic acid solution inisopropanol by weight) and a flow control additive [0.38 g of a 20%FLUORAD FC-430 (3M Company) solution in isopropanol by weight]. Themixture was stirred by using a mixer, IKA - Ultra Turrax T25, to obtaina clear enamel composition.

The enamel was applied to cold rolled steel test panels and baked at175° C. for 20 min. The film thickness was about 1.0-1.5 mil. Thecoating testings were carried out according to following standardmethods:

1. Gloss (BYK micro gloss, ASTM Method D523)

2. Hardness (Pencil Method, ASTM D3362)

3. Impact resistance (BYK-Gardner Impact Tester, ASTM D2794)

The acid etch resistance of the coatings was determined by adding a fewdrops of 10% sulfuric acid (e.g. six drops) onto the film surface of thecoated panel and baking in an oven at 50° C. for 0.5 hour. The residualacid solution was washed off and the surface observed for loss ofgloss/loss of adhesion.

The enamel had excellent gloss, chemical resistance, impact resistanceand pencil hardness. Compared to an enamel (Comparative Examples 1 and2) which was prepared from a control resin not containing thehydroxy-functionalized isophthalate ester moiety, this enamel had muchimproved hardness and acid-etch resistance (See Table 1).

Comparative Example 1-(Hydroxy Terminated Control Resin Without HydroxyFunctionalized Isophthalic Acid Component)

To a three necked round bottom flask equipped with a mechanical stirrer,a steam partial condenser, a Dean-Stark trap, and a water condenser werecharged the following reactants: NPG (86.82 g, 0.83 mole), TMP (7.98 g,0.06 mole), IPA (106.18 g, 0.64 mole), AD (29.20 g, 0.20 mole) and 0.20g of FASCAT 4100 catalyst (Atochem North America, Inc). The mixture washeated to 200° C. and stirred under a nitrogen atmosphere and held at200° C. for about 2 hours and distillate collected in the Dean-Starktrap. The temperature was increased to 220° C. and held for about 2.0additional hours and further distillate collected. The resulting viscousresin was collected in a metal container and allowed to cool to roomtemperature. The resin has the following composition based on the mol %of the components present: NPG (48.0%), TMP (3.5%), IPA (37.0%) and AD(11.5%).

Comparative Example 2 - Comparative Enamel 1 )

A portion (20.0 g) of the hydroxy enriched control resin of ComparativeExample 1 was dissolved in 40 mL of a solvent mixture (15% xylene, 70%methyl n-amyl ketone and 15% ethyl 3-ethoxypropionate). To this solutionwere added 5 g of a crosslinking agent, hexamethoxy -methyl melamine,CYMEL 303 (American Cyanamid), an acid catalyst (0.38 g of a 40%p-toluenesulfonic acid solution in isopropanol) and a flow controladditive [0.38 g of a 20% FLUORAD FC 430 (3M Company) solution inisopropanol by weight]. The mixture was stirred with a mixer for 5 min.to obtain a clear enamel composition.

The enamel was applied to a cold-rolled steel test panel and theresulting enamel tested as described in Example 2. Properties arereported in Table 1.

Example 3 - Preparation of Carboxy Terminated Resin

To a three necked round bottom flask equipped with a mechanical stirrer,a steam partial condenser, a Dean-Stark trap, and a water condenser werecharged the following reactants: NPG (79.16 g, 0.761 mole), IPA (44.24g, 0.266 mole), HIPA (43.18 g, 0.237 mole), trimellitic anhydride (16.37g, 0.085 mole) and 0.20 g of FASCAT 4100 catalyst (Atochem NorthAmerica, Inc). The mixture was heated to 150° C. and stirred under anitrogen atmosphere. The temperature was then gradually increased to200° C. and held for about 1 hour and distillate collected in the DeanStark trap. After allowing the reaction mixture to cool slightly, AD(40.97 g, 0.281 mole) was added and the polycondensation reactioncontinued by heating the mixture at 200° C. for 1.5 hours. The resultingviscous resin was collected in a metal container and allowed to cool toroom temperature. The resin has the following composition based on themol % of the components present: NPG (46.7%), IPA (16.3%), HIPA (14.6%),TMA (5.2%) and AD (17.2%).

Example 4 -Preparation of Enamel 2

A clear enamel composition was prepared from the carboxy terminatedresin prepared in Example 3 (20.0 g) exactly as described in ComparativeExample 2 and the enamel applied to a steel test panels as described inExample 2. The properties of gloss, pencil hardness and impactresistance were determined by standard methods mentioned in Example 2.The solvent resistance was also determined (ASTM Method D1308). Theresults are reported in Table II. Compared to an enamel (ComparativeExamples 3 and 4) which was prepared from a control resin not containingthe hydroxy functionalized isophthalate ester moiety, this enamel hadmuch improved impact strength, pencil hardness, and solvent resistance.

Comparative Example 3-(Carboxy Terminated Control Resin Without HydroxyFunctionalized Isophthalic Acid Component)

To a three neck round bottom flask equipped with a mechanical stirrer, asteam partial condenser, a Dean-Stark trap and a water condenser werecharged the following reactants: NPG (79.16 g,0.760 mole), IPA (83.58 g,0.500 mole), TMA (16.37 g, 0.085 mole) and 0.20 g of FASCAT 4100catalyst (Atochem North America, Inc). The mixture was heated to 180° C.and stirred under a nitrogen atmosphere. The temperature was graduallyincreased to 200° C. and held for about 2.0 hours and distillatecollected in the Dean-Stark trap. After allowing the reaction mixture tocool slightly, AD (40.97 g, 0.280 mole) was added and thepolycondensation reaction continued by heating the reaction mixture at200° C. for about 2.0 hours. The resulting viscous resin was collectedin a metal container and allowed to cool to room temperature. The resinhas the following composition based on the mol % of the componentspresent: NPG (46.8%), IPA (30.8%), TMA (5.2%) and AD (17.2%).

Comparative Example 4 (Comparative Enamel 2)

A portion (20.0 g) of the carboxy enriched control resin of ComparativeExample 3 was dissolved in 40 mL of a solvent mixture (15% xylene, 70%methyl n-amyl ketone and 15% ethyl 3-ethoxypropionate). To this solutionwas added 5 g of a crosslinking agent, hexamethoxymethyl melamine, CYMEL303 (American Cyanamid), an acid catalyst (0.38 g of a 40%p-toluenesulfonic acid solution in isopropanol) and a flow controladditive [0.38 g of a 20% FLUORAD FC- 430 (3M Company) solution inisopropanol by weight.] The mixture was stirred with a mixer for 5 min.to obtain a clear enamel composition.

The enamel was applied to a cold rolled steel test panel and theresulting enamel tested as described in Example 4. The results arereported in Table II.

Example 5 - Preparation of Water-Borne Enamel Composition

A portion (40.0 g) of the carboxy terminated resin of Example 3 washeated to 100° C. and a solvent, ethylene glycol monobutylether (10 g)was added. The resin was dispersed by adding a solution ofdimethylaminoethanol (5.0 g) in water (140 g) with good agitation at 50°C. The water dispersion was subsequently mixed with CYMEL 303 (10 g) andFLUORAD FC- 430 (20% in isopropanol, 0.6 g) to yield a water borneenamel having a pH of about 6.8.

The enamel was applied to a cold-rolled steel test panel and theresulting enamel tested as described in Example 2. The cured enamel hadgood gloss (60°/20°=102/87), excellent impact resistance (direct/reverse=160/160 lb-in) and excellent pencil hardness (4H).

                  TABLE I                                                         ______________________________________                                        PROPERTIES OF ENAMELS                                                                                  COMPARATIVE                                                                   ENAMEL 1                                                         ENAMEL 1     (COMPARATIVE                                         PROPERTY    (EXAMPLE 2)  EXAMPLE 2)                                           ______________________________________                                        Gloss 60°/20°                                                               101/90       100/89                                               Pencil Hardness                                                                           5 H          H                                                    Impact Resistance                                                                         160/160      160/160                                              Direct/Reverse                                                                (lb-in.)                                                                      Acid-Etch   No Effect    Loss of Gloss/Adhesion                               Resistance                                                                    10%H.sub.2 SO.sub.4 0.5 hr at                                                 50° C.                                                                 Stain Resistance                                                                          No Effect    Slight Effect                                        Iodine, 0.5 hr                                                                ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        PROPERTIES OF ENAMELS                                                                                  COMPARATIVE                                                                   ENAMEL 2                                                         ENAMEL 2     (COMPARATIVE                                         PROPERTY    (EXAMPLE 4)  EXAMPLE 4)                                           ______________________________________                                        Gloss 60°/20°                                                               98/81        97/61                                                Pencil Hardness                                                                           4-5 H        H                                                    Impact Resistance                                                                         160/160      <20/<20                                              Direct/Reverse                                                                (lb-in.)                                                                      Solvent     No Effect    Scratches                                            Resistance MEK                                                                Double Rub, 200                                                               ______________________________________                                    

Example 6-Preparation of High T₈ Resin for Powder Coatings

To a three-necked round bottom flask equipped with a mechanical stirrer,a steam partial condenser, a Dean-Stark trap, and a water condenser werecharged the following materials: NPG (111.54 g, 1.07 mole), TMP (5.58 g,0.04 mole), terephthalic acid (TPA) (114.99 g, 0.69 mole), HIPA (53.37g, 0.29 mole), and 0.20 g of FASCAT 4100 catalyst. The mixture washeated to 150° C. and stirred under nitrogen atmosphere. The temperaturewas then gradually increased to 220° C. and held for about 8 hours anddistillate collected in the Dean-Stark trap. The resulting viscous resinwas collected in a metal container and cooled to room temperature. Theresin has the following compositions based on the mole percent of thecomponents present: NPG (51.2%), TMP (1.9%), TPA (33.0%), and HIPA(13.9%). The resin has a T₈ of 66° C. and a number average molecularweight of 2400.

Examples of Powder Coatings from Resins with Phenolic Pendant Groups

In the Examples below, the inherent viscosity (I. V.), in dl/g weredetermined in phenol/tetrachloro -ethane (60/40 w/w ) at a concentrationof 0.5g/100 ml.

The resin melt viscosity, in poise, were determined using an ICI meltviscometer at 200° C.

The acid number and hydroxyl number were determined by titration andreported as mg of KOH consumed for each gram of resin.

The glass transition temperature (Tg), was determined by differentialscanning calorimetry (DSC) on the second heating cycle scanning rate at20° C./minute after the sample had been heated to melt and quenched tobelow the resin Tg. Tg values are reported as midpoint.

The weight average molecular weight (Mw) and number average molecularweight (Mn) were determined by gel permeation chromatography intetrahydrofuran (THF) using polystyrene standard and a UV detector.

Impact strengths were determined using a Gardner Laboratory, Inc.,impact tester per ASTM D 2794-84.

Pencil hardness was determined using ASTM D 3363-74. The hardness isreported as the hardest pencil which will not cut into the coating. Theresults are expressed according to the following scale:(softest)6B,5B,4B,3B,2B,B,HB,F,H,2H,3H,4H,5H,6H (hardest).

The conical mandrel was performed using a Gardener Laboratory Inc.,conical mandrel of specified size according to ASTM- 522.

The 20 and 60 degree gloss were measured using a gloss meter (GardenerLaboratory, Inc. Model GC- 9095) according to ASTM D- 523.

1. Hydroxyl terminated resin with 4-hydroxyisophthalic acid for powdercoating composition (Resin PC)

To a 3000 ml, 3 neck round bottom flask were added 2,2-dimethyl-1,3-propanediol (917.2 g, 8.806 moles) and FASCAT™ 4100 (2.0 g). Thecontent was heated to melt at 180° C. and terephthlic acid (1271.8 g,7.654 moles), and 4-hydroxyisophthalic acid (121.2 g, 0.666 moles) wasadded. The flask was swept with 1.0 scfh nitrogen while the temperatureswas raised from 180° C. to 230° C. over a 6-hour period. The batchtemperature was maintained at 230° C. for 8 hours. The molten resin waspoured to a syrup can where it cooled to a solid with the followingproperties:

    ______________________________________                                        I.V.                    265    dl/g                                           ICI Melt Viscosity at 200° C.                                                                  22     poise                                          Acid Number             33.8                                                  Hydroxyl number         41.0                                                  DSC (2nd cycle)                                                               Tg                      67° C.                                         Gel permeation chromatography                                                 Mw                      7,703                                                 Mn                      2,991                                                 ______________________________________                                    

2. Powder Coating Composition comprising hydroxyl terminated Resin PCand POWDERLINK™ 1174

This example provides a powder coating with superior cure, solventresistance (MEK rubs), impact resistance and conical mandrel properties.

Resin PC (376.0 g), POWDERLINK™ 1174 (24.0 g), Methyltolyl sulfonimide (5.0 g), Flow aid (6.0 g), benzoin (4.0 g), and titanium dioxide (160.0g) were mixed in a Vitamix mixer and compounded in an APV extruder at125° C. The extrudate was cooled, granulated, and pulverized in a Bantammill with liquid nitrogen bled into the grinding chamber. The powder wasclassified through a 200 mesh screen. The powder was electrostaticallyapplied to a 3 in. ×9 in. metal panel and cured in a 350° F. oven for 20minutes. The film properties are as follows:

    ______________________________________                                        Film thickness, Mil                                                                             2.2                                                         Impact strength, (in.-lb)                                                     Front             140                                                         Reverse           160                                                         Pencil Hardness   F                                                           Gloss                                                                         20 deg             74                                                         60 deg            101                                                         1/8" conical Mandrell                                                                           pass                                                        MEK double rubs   more than 200                                               ______________________________________                                    

3. Powder Coating from Commercial ARAKOTE™ 3109 (Ciba-Geigy) andPOWDERLINK™ 1174 (American Cyanamid)

This comparative example provides powder coating from a commercial resinwith less cure and thus poorer overall properties.

ARAKOTE™ 3109 (376.0 g), POWDERLINK™ 1174 (24.0 g), Methyl tolylsulfonimide (5 g), flow aid (6.0 g), benzoin (4.0 g), and titaniumdioxide (160.0 g) are mixed in a vitamix mixer and compounded in an APVextruder at 125° C. The extrudate was cooled, granulated, and pulverizedin a bantam mill with liquid nitrogen bled into the grinding chamber.The powder was classified through a 200 mesh screen. The powder waselectrostatically applied to a 3 in. ×9 in. metal panel and cured in a350° F. oven for 20 minutes. The film properties are as follows:

    ______________________________________                                        Film thickness, Mil                                                                             2.0                                                         Impact strength, (in.-lb)                                                     Front             20                                                          Reverse           less than 20                                                Pencil Hardness   F                                                           Gloss                                                                         20 deg            73                                                          60 deg            101                                                         1/8" conical Mandrell                                                                           fail                                                        MEK double rubs   less than 200                                               ______________________________________                                    

We claim:
 1. A thermosetting powder coating composition comprising(I)about 95 to 70 weight percent of a curable polyester having a numberaverage molecular weight of about 800 to about 6,000, a weight averagemolecular weight of about 3,000 to about 40,000, and a T₈ of greaterthan about 50° C., comprising (a) about 20 to about 60 mol % of diolresidues, based on the total moles of components (a), (b), (c), (d), (e)and (f); (b) 0 to about 20 mol % of polyol residues, based on the totalmoles of components (a), (b), (c), (d), (e) and (f); (c) about 5 toabout 40 mol % of hydroxy functionalized isophthalic acid residues,based on the total moles of (a), (b), (c), (d), (e) and (f); saidhydroxy functionalized residues having the formula ##STR7## wherein X isselected from --O--, --S--, --SO₂ -- or --O--(CH₂ --)_(n) (n is 1 toabout 6); R is a phenyl radical containing 1-3 hydroxy groups with theproviso that when X is --O-- or --S--, that R may also be hydrogen; (d)about 10 to about 40 mol % of diacid residues, derived from an aromaticdiacid or a cycloaliphatic diacid or a mixture thereof, based on thetotal moles of (a), (b), (c), (d), (e) and (f); (e) about 0 to about 40mol % of diacid residues derived from an aliphatic diacid, based on thetotal moles of components (a), (b), (c), (d), (e) and (f); (f) 0 toabout 10 mol % of residues derived from trimellitic acid or trimelliticanhydride, based on the total moles of components (a), (b), (c), (d),(e) and (f); and (II) about 5 to 30 weight percent of a cross-linkingagent.
 2. The composition of claim 1, wherein in the curable polyester,the component (a) diol residues are selected from the group consistingof ethylene glycol; propylene glycol; 1,3 propanediol; 2,4 dimethyl2-ethyl -hexane 1,3 diol; 2,2 dimethyl 1,3 propanediol; 2-ethyl -2-butyl1,3 propanediol; 2 ethyl 2 isobutyl 1,3 -propanediol; 1,3 butanediol;1,4 butanediol; 1,5 -pentanediol, 1,6 hexanediol; 2,2,4 trimethyl 1,3-pentanediol; thiodiethanol; 1,2 cyclohexanedimethanol;1,3-cyclohexanedimethanol; 1,4-cyclohexanedimethanol;2,2,4,4-tetramethyl 1,3 cyclobutanediol; p-xylylenediol; diethyleneglycol, triethylene glycol; tetraethylene glycol; and pentaethylene,hexaethylene, heptaethylene, octaethylene, nonaethylene, anddecaethylene glycols.
 3. The composition of claim 1, wherein in thecurable polyester, the component (b) polyol residues are selected fromresidues of the group consisting of trimethylolpropane,trimethylolethane, glycerol, 2,2-bis (hydroxymethyl)-1,3-propanediol,1,2,3,4,5,6-hexahydroxyhexane, and bis(2,2-bis(hydroxymethyl)-3-propanolether.
 4. The composition of claim 1, wherein in the curable polyester,the component (c) hydroxy functionalized isophthalic acid residues areselected from the group consisting of ##STR8##
 5. The composition ofclaim 1, wherein in the curable polyester, component (c) is comprised ofresidues of 5-hydroxyisophthalic acid.
 6. The composition of claim 1,wherein in the curable polyester, the component (d) diacid residues areselected from the group consisting of residues of isophthalic, phthalic,terephthalic, diphenic, 4,4'-oxydibenzoic, 4,4'-sulfonyldibenzoic,4,4,'-biphenyl -dicarboxylic, naphthalenedicarboxylic, 1,2-cyclohexanedicarboxylic, 1,3 cyclohexane dicarboxylic, 1,4-cyclohexanedicarboxylic, and 1,4-cyclopentane dicarboxylic acids.
 7. Thecomposition of claim 1, wherein in the curable polyester, the component(e) aliphatic diacid residues are selected from the group consisting ofoxalic, malonic, dimethylmalonic, succinic, glutaric, adipic,trimethyladipic, pimelic, 2,2-dimethylglutaric, azelaic, sebacic,fumaric, maleic, and itaconic acids.
 8. The composition of claim 1,wherein the cross-linking agent is an amino cross-linking agent.
 9. Thecomposition of claim 1, wherein the cross-linking agent is a glycouriltype cross-linking agent possessing a plurality of --N--CH₂ OR groups,wherein R=C₁ -C₈ alkyl.
 10. The composition of claim 1, wherein thecross-linking agent has the formula ##STR9##
 11. A shaped or formedarticle coated with the thermosetting powder coating composition ofclaim 1.